Shifted Pulses For Simultaneous Multi-Slice Imaging

ABSTRACT

A computer-implemented method for performing multi-slice magnetic resonance imaging with comparable contrast between simultaneously excited slices includes applying a first pulse sequence to a volume of interest to acquire a first k-space dataset. This first pulse sequence comprises a plurality of single-band slice-selective pulses applied in a first predefined order. One or more additional pulse sequences are also applied to the volume of interest to acquire one or more additional k-space datasets. Each additional pulse sequence comprises the plurality of single-band slice-selective pulses applied in one or more additional predefined orders that are distinct from the first predefined order. One or more final images are reconstructed using the first k-space dataset and the one or more additional k-space datasets.

TECHNOLOGY FIELD

The present invention relates generally to methods, systems, andapparatuses for performing simultaneous multi-slice Magnetic ResonanceImaging (MRI) using single-band pulses in a manner that provides similarcontrast to multi-band applications.

BACKGROUND

Simultaneous multi-slice (SMS) is an acceleration technique in whichseveral slices are excited and acquired simultaneously leading to ak-space dataset which comprising several slices collapsed on top of eachother. Separating or uncollapsing these slices is performed during imagereconstruction with the slice GeneRalized Autocalibrating PartialParallel Acquisition (GRAPPA) method. Excitation, refocusing ormagnetization preparation (mag-prep) for these simultaneously acquiredslices is performed using a multi-band radio frequency (RF) pulse, asshown in FIG. 2A. A multi-band RF pulse is generated by superposition ofthe individual single band RF pulses which are typically used toexcite/refocus/mag-prep a single slice in conventional MRI. Using amulti band RF pulse ensures that imaging parameters like echo time (TE),inversion time (TI) etc. are identical for all the simultaneouslyacquired slices.

One drawback of using a multi-band RF pulse is the increase in peak RFpower which increases by a factor equal to the number of simultaneouslyacquired slices (due to superposition as shown in FIG. 2A). The higherpeak power requirement is typically not a problem for excitation pulses,but can become a prohibiting factor for refocusing or magnetizationpreparation (saturation recovery, inversion recovery, Driven EquilibriumFourier Transform (DEFT) magnetization restore etc.) pulses.

Various techniques have been proposed for addressing the problem of peakRF power for SMS imaging including VErsatile Reaction SEparation(VERSE), the use of phase scrambling during imaging, and the use oftime-shifted multi-band pulses during imaging. Each of these techniqueshas significant drawbacks that limit their general applicability toclinical imaging scenarios. For example, the VERSE technique leads todistorted slice profiles for off-resonance spins. Moreover, each ofthese techniques still requires a peak power value which is higher thanthat needed for a single band RF pulse. This can still pose a problemfor high power pulses like adiabatic inversion with a hyperbolic secantpulse, or adiabatic saturation pulses, or DEFT restore pulses used inSMS TSE imaging etc.

SUMMARY

Embodiments of the present invention address and overcome one or more ofthe above shortcomings and drawbacks, by providing methods, systems, andapparatuses related to the use of shifted pulses for simultaneousmulti-slice imaging. The techniques described herein require the samepeak power as a single band RF pulse and, thus may be applied to highpower magnetization preparation pulses including, without limitation,adiabatic inversion with a hyperbolic secant pulse, adiabatic saturationpulses, or DEFT restore pulses used in SMS TSE imaging.

According to some embodiments, A computer-implemented method forperforming multi-slice magnetic resonance imaging with comparablecontrast between simultaneously excited slices includes applying a firstpulse sequence to a volume of interest to acquire a first k-spacedataset. This first pulse sequence comprises a plurality of single-bandslice-selective pulses applied in a first predefined order. One or moreadditional pulse sequences are also applied to the volume of interest toacquire one or more additional k-space datasets. Each additional pulsesequence comprises the plurality of single-band slice-selective pulsesapplied in one or more additional predefined orders that are distinctfrom the first predefined order. In some embodiments, the additionalpredefined orders are defined by cyclically shifting the firstpredefined order to yield an average inversion time (TI) for all slicesin the volume of interest. One or more final images are reconstructedusing the first k-space dataset and the one or more additional k-spacedatasets.

Various techniques may be used for reconstructing the k-space datasets.For example, in some embodiments of the aforementioned method, finalimages are reconstructed by averaging the k-space datasets to yield acombined k-space dataset and then reconstructing the final images usingthe combined k-space dataset. In other embodiments, the final images arereconstructed by reconstructing a plurality of images, with each imagecorresponding to one of the datasets. The final images are generated byaveraging each of these images.

Various pulse sequences may be used with the aforementioned method. Insome embodiments, the pulse sequences each utilize Short-TI InversionRecovery (STIR) to null fat in the volume of interest. In otherembodiments, the pulse sequences are each a Turbo Inversion RecoveryMagnitude (TIRM) sequence. In still other embodiments, the pulsesequences are each a DEFT sequence. The number of pulses included ineach pulse sequence may be selected, for example, based on a SMS factorselected by a user.

In some embodiments of the aforementioned method, pulse sequences eachfurther comprise a plurality of multi-band slice-selective excitationpulses. Additionally, the pulse sequences may comprise multi-bandslice-selective refocusing pulses.

According to other embodiments of the present invention, acomputer-implemented method for performing multi-slice magneticresonance imaging includes acquiring a k-space dataset representative ofa volume of interest using an acquisition process. This acquisitionprocess includes the application of single-band slice-selective pulsesto the volume of interest. These single-band slice-selective pulses arespaced according to a predefined echo spacing period selected to providean identical inversion time for each of the plurality of single-bandslice-selective pulses. The method further includes applying single-bandslice-selective excitation pulses to the volume of interest. Thesesingle-band slice-selective excitation pulses are spaced according tothe predefined echo spacing period. In some embodiments, followingapplication of the single-band slice-selective excitation pulses,multi-band slice-selective pulses are applied to the volume of interest.The k-space dataset is generated using a plurality of echo trainsresulting from the plurality of single-band slice-selective excitationpulses. Then, one or more images are reconstructed image based on thek-space dataset.

According to other embodiments, a system for performing multi-slicemagnetic resonance imaging with comparable contrast betweensimultaneously excited slices comprises a RF generator and an imageprocessing computer. The RF generator is configured to use RF coils toapply a first pulse sequence to a volume of interest to acquire a firstk-space dataset. This first pulse sequence includes a plurality ofsingle-band slice-selective pulses applied in a first predefined order.The RF generator additionally applies one or more additional pulsesequences to the volume of interest to acquire one or more additionalk-space datasets. Each additional pulse sequence comprises the pluralityof single-band slice-selective pulses applied in one or more additionalpredefined orders that are distinct from the first predefined order. Insome embodiments, each of the additional predefined orders is defined bycyclically shifting the first predefined order to yield an average TIfor all slices in the volume of interest. Once the data is acquired, theimage processing computer reconstructs one or more images based on thefirst k-space dataset and the one or more additional k-space datasets.

Various pulse sequences may be used with the aforementioned system. Forexample, in some embodiments, pulse sequences each utilize STIR to nullfat in the volume of interest. In other embodiments, the pulse sequencesare each a TIRM sequence. In still other embodiments, the pulsesequences are each a DEFT sequence. The pulse sequences may each furthercomprise a plurality of multi-band slice-selective excitation pulses.Additionally, the pulse sequences may each further comprise a pluralityof multi-band slice-selective refocusing pulses. The number of pulsesincluded in each pulse sequence may be based, for example, on aSimultaneous Multi-Slice (SMS) factor selected by a user.

According to another aspect of the present invention, a system forperforming multi-slice magnetic resonance comprises a Radio Frequency(RF) generator and an image processing computer. The RF generator isconfigured to use a plurality of RF coils to apply a plurality ofsingle-band slice-selective pulses to a volume of interest. Thesingle-band slice-selective pulses are spaced according to a predefinedecho spacing period selected to provide an identical inversion time foreach of the plurality of single-band slice-selective pulses. The RFgenerator is further configured to apply a plurality of single-bandslice-selective excitation pulses to the volume of interest. Thesesingle-band slice-selective excitation pulses are spaced according tothe predefined echo spacing period. A k-space dataset representative ofthe volume of interest is acquired using a plurality of echo trainsresulting from the plurality of single-band slice-selective excitationpulses. In some embodiments, the plurality of RF coils is further usedto apply a plurality of multi-band slice-selective pulses to the volumeof interest, following application of the plurality of single-bandslice-selective excitation pulses and one or more single band refocusingpulses between the single-band slice-selective excitation pulses. Theimage processing computer is configured to reconstruct an image based onthe k-space dataset.

Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeembodiments that proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention are bestunderstood from the following detailed description when read inconnection with the accompanying drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentsthat are presently preferred, it being understood, however, that theinvention is not limited to the specific instrumentalities disclosed.Included in the drawings are the following Figures:

FIG. 1 shows a system for ordering acquisition of frequency domaincomponents representing magnetic resonance image data for storage in ak-space storage array, as used by some embodiments of the presentinvention;

FIG. 2A provides an illustration of a conventional SMS multi band RFpulse;

FIG. 2B illustrates the sequential placement of single band RF pulses intime to create similar RF profile as the multi band RF pulse but with alower peak power;

FIG. 3A illustrates a pulse sequence according to some embodiments wherethere is complete separation of the pulses;

FIG. 3B illustrates a pulse sequence according to some embodiments wherethere is three partially overlapping pulses;

FIG. 4A illustrate a technique for providing comparable contrast betweenthe simultaneously excited slices, according to some embodiments;

FIG. 4B provides a continuation of the technique illustrated in FIG. 4A;

FIG. 5 illustrates a second technique for providing comparable contrastbetween the simultaneously excited slices, according to someembodiments, where a single average is used; and

FIG. 6 illustrates an exemplary computing environment within whichembodiments of the invention may be implemented.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following disclosure describes the present invention according toseveral embodiments directed at methods, systems, and apparatusesrelated to using shifted pulses for simultaneous multi-slice imaging. Insome embodiments, individual single-band RF pulses are playedconsecutively in time in order to sequentially alter the magnetizationof slices which are being acquired simultaneously. In other embodiments,multiple pulse sequences are used during image acquisition and averagingis used to provide comparable contrast across slices. Other embodiments,utilize a predefined echo spacing between individual inversion recovery(IR) pulses, while also using the same echo spacing between excitationpulses, to provide identical T1 contrast across slices. These techniqueshave the advantage of requiring the same peak power as a single band RFpulse and lower peak power compared to conventional solutions.

FIG. 1 shows a system 100 for ordering acquisition of frequency domaincomponents representing magnetic resonance imaging (MRI) data forstorage in a k-space storage array, as used by some embodiments of thepresent invention. In system 100, magnetic coils 12 create a static basemagnetic field in the body of patient 11 to be imaged and positioned ona table. Within the magnet system are gradient coils 14 for producingposition dependent magnetic field gradients superimposed on the staticmagnetic field. Gradient coils 14, in response to gradient signalssupplied thereto by a gradient and shim coil control module 16, produceposition dependent and shimmed magnetic field gradients in threeorthogonal directions and generates magnetic field pulse sequences. Theshimmed gradients compensate for inhomogeneity and variability in an MRIdevice magnetic field resulting from patient anatomical variation andother sources. The magnetic field gradients include a slice-selectiongradient magnetic field, a phase-encoding gradient magnetic field and areadout gradient magnetic field that are applied to patient 11.

Further RF module 20 provides RF pulse signals to RF coil 18, which inresponse produces magnetic field pulses which rotate the spins of theprotons in the imaged body of the patient 11 by ninety degrees or by onehundred and eighty degrees for so-called “spin echo” imaging, or byangles less than or equal to 90 degrees for so-called “gradient echo”imaging. Gradient and shim coil control module 16 in conjunction with RFmodule 20, as directed by central control unit 26, controlslice-selection, phase-encoding, readout gradient magnetic fields, radiofrequency transmission, and magnetic resonance signal detection, toacquire magnetic resonance signals representing planar slices of patient11.

In response to applied RF pulse signals, the RF coil 18 receivesmagnetic resonance signals, i.e., signals from the excited protonswithin the body as they return to an equilibrium position established bythe static and gradient magnetic fields. The magnetic resonance signalsare detected and processed by a detector within RF module 20 and k-spacecomponent processor unit 34 to provide a magnetic resonance dataset toan image data processor for processing into an image. In someembodiments, the image data processor is located in central control unit26. However, in other embodiments such as the one depicted in FIG. 1,the image data processor is located in a separate unit 27.Electrocardiography (ECG) synchronization signal generator 30 providesECG signals used for pulse sequence and imaging synchronization. A twoor three dimensional k-space storage array of individual data elementsin k-space component processor unit 34 stores corresponding individualfrequency components comprising a magnetic resonance dataset. Thek-space array of individual data elements has a designated center andindividual data elements individually have a radius to the designatedcenter.

A magnetic field generator (comprising coils 12, 14, and 18) generates amagnetic field for use in acquiring multiple individual frequencycomponents corresponding to individual data elements in the storagearray. The individual frequency components are successively acquired inan order in which radius of respective corresponding individual dataelements increases and decreases along a substantially spiral path asthe multiple individual frequency components are sequentially acquiredduring acquisition of a magnetic resonance dataset representing amagnetic resonance image. A storage processor in the k-space componentprocessor unit 34 stores individual frequency components acquired usingthe magnetic field in corresponding individual data elements in thearray. The radius of respective corresponding individual data elementsalternately increases and decreases as multiple sequential individualfrequency components are acquired. The magnetic field acquiresindividual frequency components in an order corresponding to a sequenceof substantially adjacent individual data elements in the array andmagnetic field gradient change between successively acquired frequencycomponents which are substantially minimized.

Central control unit 26 uses information stored in an internal databaseto process the detected magnetic resonance signals in a coordinatedmanner to generate high quality images of a selected slice(s) of thebody (e.g., using the image data processor) and adjusts other parametersof system 100. The stored information comprises predetermined pulsesequence and magnetic field gradient and strength data as well as dataindicating timing, orientation and spatial volume of gradient magneticfields to be applied in imaging. Generated images are presented ondisplay 40 of the operator interface. Computer 28 of the operatorinterface includes a graphical user interface (GUI) enabling userinteraction with central control unit 26 and enables user modificationof magnetic resonance imaging signals in substantially real time.Continuing with reference to FIG. 1, display processor 37 processes themagnetic resonance signals to reconstruct one or more images forpresentation on display 40, for example. Various techniques generallyknown in the art may be used for reconstruction.

FIG. 2B illustrates the sequential placement of single band RF pulses intime to create similar RF profile as the multi band RF pulse but with alower peak power. As shown in FIG. 2B, the individual single-band RFpulses are played consecutively in time in order to sequentially alterthe magnetization of slices which are being acquired simultaneously.This technique has the advantage that it requires the same peak power asa single band RF pulse and hence is applicable to high powermagnetization preparation pulses like adiabatic inversion with ahyperbolic secant pulse, or adiabatic saturation pulses, or DEFT restorepulses used in SMS TSE imaging etc. The technique shown in FIG. 2B willbecome of special importance to enable SMS techniques for futurelow-cost systems where the peak RF power is expected to be limited.

In conventional imaging with magnetization preparation, there is apreparation pulse for a slice following by a waiting time and readout isperformed. Using the technique shown in FIG. 2B, a readout for 3 slicesis performed simultaneously. Thus, three single band preparation pulsesare applied successfully in a brief time period (e.g., 20 ms). This isfollowed by the normal waiting time and the readout of the three slicessimultaneously, as in the conventional system. The phase shown in FIG.2B is essentially a concatenation of the three phases shown in FIG. 2A.It should be noted that the change in phase shown in FIG. 2B allows thecenter of frequency of the pulses (i.e., the Larmor frequency) to beconstant. As an alternative, in other embodiments, the center frequencyof each pulse is varied in a manner that supports slice selection whilephase is kept constant (or near constant) across all pulses.

The brief time period allows any motion in the region of interest to benegligible during imaging. Timing effects can also be minimized byacquiring data in different slice orders and averaging the results. Forexample, for the simple case of an SMS acquisition with a multibandfactor of 2, the first slice may be prepared followed by the secondslice. Then, a second acquisition can be performed with the slicepreparation order reversed (i.e., preparing the second slice first). Theresults may then be averaged to eliminate motion artifacts to someextent. This general concept can be extended to high multiband factors,using different permutations of slice acquisitions across for eachacquisition sequence that is performed.

Since the limited peak power becomes a limiting factor (especially forthe pulse main lobe), it is also possible to separate the pulses notcompletely in time but instead shift the respective pulses in a way thatonly their side lobes overlap and the main lobes are still separated.FIGS. 3A and 3B illustrate how this overlap could be implemented in someembodiments. More specifically, FIG. 3A shows complete separation of thepulses (similar sequence discussed above with reference to FIG. 2B),while FIG. 3B shows three partially overlapping pulses. The magnitudeand phase of each pulse may be set in a manner which is similar to thatdiscussed above with reference to FIG. 2B.

In general, the pulses illustrated in FIG. 3B may be overlapped to anydegree desired. However, in the extreme case where the pulses fullyoverlap, the acquisition is essentially identical to the conventionalmulti-band acquisition shown in FIG. 2A. Thus, to provide the benefitsof minimizing the peak power requirement, the degree of overlap shouldgenerally be set to a value which ensures that the desired peak powerwill be achieved. In some embodiments, the degree of overlap may beselected by the operator of the scanner (e.g., by inputting a value orusing slider in a graphical user interface). In this way, the operatorhas the flexibility to tailor the peak power as desired based on factorssuch as the capabilities of the hardware and type of scan beingperformed.

In some embodiments, the acquisition sequence comprises a plurality ofsections, each with differently designed multi-band pulses. For example,a multi-band IR TSE sequence combined with a DEFT restore pulse maycomprise IR pulses which are played out as single-band pulses for theindividual slices as proposed in the techniques discussed herein, anecho train comprising conventionally superimposed multi-band RFexcitation, refocussing pulses, and finally single-band DEFT restorepulses for the individual slices.

A potential drawback of the proposed method is that the imagingparameters like TE, TI etc. are slightly different for each individualslice; this effect is expected to be negligible for some applications,especially for clinically feasible SMS factors in the range of 2 to 4.For example, the TI for a fluid attenuation inversion recovery (FLAIR)brain examination is approximately 2500 ms. A shift of the pulses willonly lead to a change in TI which is two orders of magnitude below thisvalue and is thus not expected to have a relevant impact. A change inthe timing of DEFT magnetization restore pulses is also expected to haveonly minimal impact as the next data acquisition of the respective slicewill only occur after another TR period which is also at least twoorders of magnitude above the time shift between two DEFT pulses.

For other applications the impact of the proposed method on the imagecontrast might become significant. In some embodiments of the presentinvention, pulses sequences may be utilized which shift pulses toprovide comparable contrast between the simultaneously excited slices.This may be of special interest for, for example, in Short-TI InversionRecovery (STIR) and Turbo Inversion Recovery Magnitude (TIRM) imaging ofbody regions like abdomen, breast, joints or heart where the TI timestypically are around 150-250 ms and, thus, a time shifting of pulses hasa bigger influence on contrast than for FLAIR imaging in the brain (TIaround 2-3 seconds)

FIGS. 4A and 4B illustrate a first technique for providing comparablecontrast between the simultaneously excited slices, according to someembodiments. This technique may be applied, for example, in IR or DEFTapplications. In this example, two slices are acquired using twosequences which vary according to the order in which the slice selectivepulses are applied. More specifically, in FIG. 4A the pulse sequencecomprises plurality of single-band slice-selective IR pulses applied ina predefined order where the first IR pulse is applied to the firstslice and then the subsequent pulse is applied to the second slice. InFIG. 4B, the order is reversed such that the first IR pulse is appliedto the second slice and then the subsequent pulse is applied to thefirst slice. For each sequence, the IR pulses are followed by multi-bandslice-selective excitation and refocusing pulses which result insimultaneous echoes from the individual slices. These echoes are used toproduce a k-space dataset for each sequence (i.e., application of FIG.4A results in a k-space dataset and FIG. 4B results in a seconddataset). The datasets are then averaged to produce a combined datasetwhich can be used to reconstruct an image for each slice. In anotherembodiment, the datasets are reconstructed first and the final images ofthe first repetition depicted in FIG. 4A and the second repetitiondepicted in FIG. 4B are averaged in a final step.

Although FIGS. 4A and 4B illustrate the averaging technique for 2pulses, it should be understood that technique may be scaled to largernumbers of pulses based on the SMS factor selected, for example, by theoperator. If the averaging is performed with data equal to SMS factor,the shifts between each sequence can be cyclic to come up with anaverage TI time for all slices without exceeding peak powerrequirements. If the number of averages is lower than the SMS factor,only some permutations can be performed. For the example of an SMSfactor of 3 and 2 averages, the pulses can be played out in temporalorder for slice 1, slice 2, slice 3 in the first run and in temporalorder slice 3, slice 2, slice 1 in the second run. Here, TI for slice 2stays identical for both repetitions while TI for slices 1 and slice 3are interchanged and will become comparable to TI for slice 2 afteraveraging has been performed.

FIG. 5 illustrates a second technique for providing comparable contrastbetween the simultaneously excited slices, according to someembodiments, where a single average is used. In this example, identicalTI is achieved for each IR pulse by shifting the echo trains for slices1 and 2 against each other and by time-shifting the IR pulses by thatpredefined the echo spacing (ES). The influence of the IR contrast willbe much more prominent than the T₂ contrast such that the contrastbetween both slices should be more similar to that achieved when usingdifferent TI times for both slices.

In the example of FIG. 5, two single-band slice-selective IR pulses areapplied to the volume of interest. These two pulses are spaced based onthe ES period, as discussed above. Following application of the IRpulses, slice-selective excitation pulses are applied to the volume ofinterest, again spaced by the ES period. Shifting the excitation pulsesresulting in a shift to the echo trains by the amount of time betweenthe inversion/saturation pulses. In turn, this allows the TI to be thesame for both pulses. Note that, for completeness, FIG. 5 additionallyshows multi-band refocusing pulses applied to the slices as soon as thesecond slice has been excited. Between the excitation pulses for slice 1and slice 2, on or more single-band refocusing pulses can be used torefocus only the magnetization of slice 1 which already has beenexcited.

FIG. 6 illustrates an exemplary computing environment 600 within whichembodiments of the invention may be implemented. For example, thecomputing environment 600 may be used to implement one or more of thecomponents illustrated in the system 100 of FIG. 1. The computingenvironment 600 may include computer system 610, which is one example ofa computing system upon which embodiments of the invention may beimplemented. Computers and computing environments, such as computersystem 610 and computing environment 600, are known to those of skill inthe art and thus are described briefly here.

As shown in FIG. 6, the computer system 610 may include a communicationmechanism such as a bus 621 or other communication mechanism forcommunicating information within the computer system 610. The computersystem 610 further includes one or more processors 620 coupled with thebus 621 for processing the information. The processors 620 may includeone or more central processing units (CPUs), graphical processing units(GPUs), or any other processor known in the art.

The computer system 610 also includes a system memory 630 coupled to thebus 621 for storing information and instructions to be executed byprocessors 620. The system memory 630 may include computer readablestorage media in the form of volatile and/or nonvolatile memory, such asread only memory (ROM) 631 and/or random access memory (RAM) 632. Thesystem memory RAM 632 may include other dynamic storage device(s) (e.g.,dynamic RAM, static RAM, and synchronous DRAM). The system memory ROM631 may include other static storage device(s) (e.g., programmable ROM,erasable PROM, and electrically erasable PROM). In addition, the systemmemory 630 may be used for storing temporary variables or otherintermediate information during the execution of instructions by theprocessors 620. A basic input/output system (BIOS) 633 containing thebasic routines that help to transfer information between elements withincomputer system 610, such as during start-up, may be stored in ROM 631.RAM 632 may contain data and/or program modules that are immediatelyaccessible to and/or presently being operated on by the processors 620.System memory 630 may additionally include, for example, operatingsystem 634, application programs 635, other program modules 636 andprogram data 637.

The computer system 610 also includes a disk controller 640 coupled tothe bus 621 to control one or more storage devices for storinginformation and instructions, such as a hard disk 641 and a removablemedia drive 642 (e.g., floppy disk drive, compact disc drive, tapedrive, and/or solid state drive). The storage devices may be added tothe computer system 610 using an appropriate device interface (e.g., asmall computer system interface (SCSI), integrated device electronics(IDE), Universal Serial Bus (USB), or FireWire).

The computer system 610 may also include a display controller 665coupled to the bus 621 to control a display 666, such as a cathode raytube (CRT) or liquid crystal display (LCD), for displaying informationto a computer user. The computer system includes an input interface 660and one or more input devices, such as a keyboard 662 and a pointingdevice 661, for interacting with a computer user and providinginformation to the processor 620. The pointing device 661, for example,may be a mouse, a trackball, or a pointing stick for communicatingdirection information and command selections to the processor 620 andfor controlling cursor movement on the display 666. The display 666 mayprovide a touch screen interface which allows input to supplement orreplace the communication of direction information and commandselections by the pointing device 661.

The computer system 610 may perform a portion or all of the processingsteps of embodiments of the invention in response to the processors 620executing one or more sequences of one or more instructions contained ina memory, such as the system memory 630. Such instructions may be readinto the system memory 630 from another computer readable medium, suchas a hard disk 641 or a removable media drive 642. The hard disk 641 maycontain one or more datastores and data files used by embodiments of thepresent invention. Datastore contents and data files may be encrypted toimprove security. The processors 620 may also be employed in amulti-processing arrangement to execute the one or more sequences ofinstructions contained in system memory 630. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions. Thus, embodiments are not limited to any specificcombination of hardware circuitry and software.

As stated above, the computer system 610 may include at least onecomputer readable medium or memory for holding instructions programmedaccording to embodiments of the invention and for containing datastructures, tables, records, or other data described herein. The term“computer readable medium” as used herein refers to any medium thatparticipates in providing instructions to the processor 620 forexecution. A computer readable medium may take many forms including, butnot limited to, non-volatile media, volatile media, and transmissionmedia. Non-limiting examples of non-volatile media include opticaldisks, solid state drives, magnetic disks, and magneto-optical disks,such as hard disk 641 or removable media drive 642. Non-limitingexamples of volatile media include dynamic memory, such as system memory630. Non-limiting examples of transmission media include coaxial cables,copper wire, and fiber optics, including the wires that make up the bus621. Transmission media may also take the form of acoustic or lightwaves, such as those generated during radio wave and infrared datacommunications.

The computing environment 600 may further include the computer system610 operating in a networked environment using logical connections toone or more remote computers, such as remote computer 680. Remotecomputer 680 may be a personal computer (laptop or desktop), a mobiledevice, a server, a router, a network PC, a peer device or other commonnetwork node, and typically includes many or all of the elementsdescribed above relative to computer system 610. When used in anetworking environment, computer system 610 may include modem 672 forestablishing communications over a network 671, such as the Internet.Modem 672 may be connected to bus 621 via user network interface 670, orvia another appropriate mechanism.

Network 671 may be any network or system generally known in the art,including the Internet, an intranet, a local area network (LAN), a widearea network (WAN), a metropolitan area network (MAN), a directconnection or series of connections, a cellular telephone network, orany other network or medium capable of facilitating communicationbetween computer system 610 and other computers (e.g., remote computer680). The network 671 may be wired, wireless or a combination thereof.Wired connections may be implemented using Ethernet, Universal SerialBus (USB), RJ-11 or any other wired connection generally known in theart. Wireless connections may be implemented using Wi-Fi, WiMAX, andBluetooth, infrared, cellular networks, satellite or any other wirelessconnection methodology generally known in the art. Additionally, severalnetworks may work alone or in communication with each other tofacilitate communication in the network 671.

The embodiments of the present disclosure may be implemented with anycombination of hardware and software. In addition, the embodiments ofthe present disclosure may be included in an article of manufacture(e.g., one or more computer program products) having, for example,computer-readable, non-transitory media. The media has embodied therein,for instance, computer readable program code for providing andfacilitating the mechanisms of the embodiments of the presentdisclosure. The article of manufacture can be included as part of acomputer system or sold separately.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

An executable application, as used herein, comprises code or machinereadable instructions for conditioning the processor to implementpredetermined functions, such as those of an operating system, a contextdata acquisition system or other information processing system, forexample, in response to user command or input. An executable procedureis a segment of code or machine readable instruction, sub-routine, orother distinct section of code or portion of an executable applicationfor performing one or more particular processes. These processes mayinclude receiving input data and/or parameters, performing operations onreceived input data and/or performing functions in response to receivedinput parameters, and providing resulting output data and/or parameters.

A graphical user interface (GUI), as used herein, comprises one or moredisplay images, generated by a display processor and enabling userinteraction with a processor or other device and associated dataacquisition and processing functions. The GUI also includes anexecutable procedure or executable application. The executable procedureor executable application conditions the display processor to generatesignals representing the GUI display images. These signals are suppliedto a display device which displays the image for viewing by the user.The processor, under control of an executable procedure or executableapplication, manipulates the GUI display images in response to signalsreceived from the input devices. In this way, the user may interact withthe display image using the input devices, enabling user interactionwith the processor or other device.

The functions and process steps herein may be performed automatically orwholly or partially in response to user command. An activity (includinga step) performed automatically is performed in response to one or moreexecutable instructions or device operation without user directinitiation of the activity.

The system and processes of the figures are not exclusive. Othersystems, processes and menus may be derived in accordance with theprinciples of the invention to accomplish the same objectives. Althoughthis invention has been described with reference to particularembodiments, it is to be understood that the embodiments and variationsshown and described herein are for illustration purposes only.Modifications to the current design may be implemented by those skilledin the art, without departing from the scope of the invention. Asdescribed herein, the various systems, subsystems, agents, managers andprocesses can be implemented using hardware components, softwarecomponents, and/or combinations thereof. No claim element herein is tobe construed under the provisions of 35 U.S.C. 112, sixth paragraph,unless the element is expressly recited using the phrase “means for.”

We claim:
 1. A computer-implemented method for performing multi-slicemagnetic resonance imaging with comparable contrast betweensimultaneously excited slices, the method comprising: applying a firstpulse sequence to a volume of interest to acquire a first k-spacedataset, the first pulse sequence comprising a plurality of single-bandslice-selective pulses applied in a first predefined order; applying oneor more additional pulse sequences to the volume of interest to acquireone or more additional k-space datasets, each additional pulse sequencecomprising the plurality of single-band slice-selective pulses appliedin one or more additional predefined orders that are distinct from thefirst predefined order; and reconstructing one or more final imagesusing the first k-space dataset and the one or more additional k-spacedatasets.
 2. The method of claim 1, wherein the one or more final imagesare reconstructed by: averaging the first k-space dataset and the one ormore additional k-space datasets to yield a combined k-space dataset;and reconstructing the one or more final images using the combinedk-space dataset.
 3. The method of claim 1, wherein the one or more finalimages are reconstructed by: reconstructing a plurality of images usingthe first k-space dataset and the one or more additional k-spacedatasets, each image corresponding to a distinct dataset; averaging theplurality of images to yield the one or more final images.
 4. The methodof claim 1, wherein each of the one or more additional predefined ordersare defined by cyclically shifting the first predefined order to yieldan average inversion time (TI) for all slices in the volume of interest.5. The method of claim 1, wherein the first pulse sequence and the oneor more additional pulse sequences each utilize Short-TI InversionRecovery (STIR) to null fat in the volume of interest.
 6. The method ofclaim 1, wherein the first pulse sequence and the one or more additionalpulse sequences are each a Turbo Inversion Recovery Magnitude (TIRM)sequence.
 7. The method of claim 1, wherein the first pulse sequence andthe one or more additional pulse sequences are each a Driven EquilibriumFourier Transform (DEFT) sequence.
 8. The method of claim 1, wherein thefirst pulse sequence and the one or more additional pulse sequences eachfurther comprise a plurality of multi-band slice-selective excitationpulses.
 9. The method of claim 8, wherein the first pulse sequence andthe one or more additional pulse sequences each further comprise aplurality of multi-band slice-selective refocusing pulses.
 10. Themethod of claim 1, where the number of pulses included in each of thefirst pulse sequence and the one or more additional pulse sequences isbased on a Simultaneous Multi-Slice (SMS) factor selected by a user. 11.A computer-implemented method for performing multi-slice magneticresonance imaging, the method comprising: acquiring a k-space datasetrepresentative of a volume of interest using an acquisition processcomprising: applying a plurality of single-band slice-selective pulsesto the volume of interest, wherein the plurality of single-bandslice-selective pulses are spaced according to a predefined echo spacingperiod selected to provide an identical inversion time for each of theplurality of single-band slice-selective pulses, applying a plurality ofsingle-band slice-selective excitation pulses to the volume of interest,wherein the plurality of single-band slice-selective excitation pulsesare spaced according to the predefined echo spacing period, andgenerating the k-space dataset using a plurality of echo trainsresulting from the plurality of single-band slice-selective excitationpulses; and reconstructing an image based on the k-space dataset. 12.The method of claim 11, wherein the acquisition process furthercomprises: following application of the plurality of single-bandslice-selective excitation pulses, applying a plurality of multi-bandslice-selective pulses to the volume of interest.
 13. A system forperforming multi-slice magnetic resonance imaging with comparablecontrast between simultaneously excited slices, the system comprising: aRadio Frequency (RF) generator configured to use a plurality of RF coilsto: apply a first pulse sequence to a volume of interest to acquire afirst k-space dataset, the first pulse sequence comprising a pluralityof single-band slice-selective pulses applied in a first predefinedorder; apply one or more additional pulse sequences to the volume ofinterest to acquire one or more additional k-space datasets, eachadditional pulse sequence comprising the plurality of single-bandslice-selective pulses applied in one or more additional predefinedorders that are distinct from the first predefined order; an imageprocessing computer configured to reconstruct one or more images basedon the first k-space dataset and the one or more additional k-spacedatasets.
 14. The system of claim 13, wherein each of the one or moreadditional predefined orders are defined by cyclically shifting thefirst predefined order to yield an average inversion time (TI) for allslices in the volume of interest.
 15. The system of claim 13, whereinthe first pulse sequence and the one or more additional pulse sequenceseach utilize Short-TI Inversion Recovery (STIR) to null fat in thevolume of interest.
 16. The system of claim 13, wherein the first pulsesequence and the one or more additional pulse sequences are each a TurboInversion Recovery Magnitude (TIRM) sequence.
 17. The system of claim13, wherein the first pulse sequence and the one or more additionalpulse sequences are each a Driven Equilibrium Fourier Transform (DEFT)sequence.
 18. The system of claim 13, wherein the first pulse sequenceand the one or more additional pulse sequences each further comprise aplurality of multi-band slice-selective excitation pulses.
 19. Thesystem of claim 18, wherein the first pulse sequence and the one or moreadditional pulse sequences each further comprise a plurality ofmulti-band slice-selective refocusing pulses.
 20. The system of claim13, where the number of pulses included in each of the first pulsesequence and the one or more additional pulse sequences is based on aSimultaneous Multi-Slice (SMS) factor selected by a user.
 21. A systemfor performing multi-slice magnetic resonance, the system comprising: aRadio Frequency (RF) generator configured to use a plurality of RF coilsto: apply a plurality of single-band slice-selective pulses to a volumeof interest, wherein the plurality of single-band slice-selective pulsesare spaced according to a predefined echo spacing period selected toprovide an identical inversion time for each of the plurality ofsingle-band slice-selective pulses, apply a plurality of single-bandslice-selective excitation pulses to the volume of interest, wherein theplurality of single-band slice-selective excitation pulses are spacedaccording to the predefined echo spacing period, and acquire a k-spacedataset representative of the volume of interest using a plurality ofecho trains resulting from the plurality of single-band slice-selectiveexcitation pulses; and an image processing computer configured toreconstruct an image based on the k-space dataset.
 22. The system ofclaim 21, wherein the plurality of RF coils is further used to: apply aplurality of multi-band slice-selective pulses to the volume ofinterest, following application of the plurality of single-bandslice-selective excitation pulses and one or more single band refocusingpulses between the single-band slice-selective excitation pulses.